Electrochemical Impedance Spectroscopy (EIS)

Electrochemical impedance spectroscopy (EIS) determines the dielectric properties of materials. This is measured by the external field’s interaction with the dipole moment of a particular sample, usually stated by permittivity.

It is also regarded as an experimental technique that describes electrochemical systems. This method gauges system impedance over a series of frequencies. Thus, frequency response involving dissipation properties and energy storage is disclosed. Most of the time, data gathered through electrochemical impedance spectroscopy is graphically conveyed in Nyquist plots and Bode plots.

Electrochemical impedance spectroscopy is also known as dielectric spectroscopy.

Corrosionpedia explains Electrochemical Impedance Spectroscopy (EIS)

The majority of physio-chemical structures like oscillators and electro-chemical cells as well as biological tissues have dissipation properties and energy storage. Electrochemical impedance spectroscopy serves as the method to measure or evaluate them.

Impedance is the opposition that exists to the alternating current flow within a critical system. A passive form of electrical system is composed of both a resistor, or energy dissipater, and capacitor, or energy storage elements. If the system is completely resistive, AC opposition to DC is resistance.

Electrochemical impedance is typically measured with the use of a tiny excitation signal, so the response of the cell is falsely linear. In this system, the response to sinusoidal potential is a sinusoid in similar frequency. These frequencies can be represented through the Bode and Nyquist plots.

Measuring EIS is very time consuming and may take many hours. With this method, the system under measurement should be at a constant state throughout the required time to gauge the EIS spectrum. System drift is a common problem in this type of measurement and analysis.

In practice, it is hard to achieve a steady state due to several factors, such as:

Impurities

Oxide layer growth

Reaction product buildup

Degradation of coating

Changes in temperature

This method has tremendously developed over the years. It is currently broadly employed in various scientific fields like biomolecular interaction, fuel cell testing and microstructural definition. Oftentimes, this technique reveals information regarding the electrochemical process reaction mechanism. This describes the fact that various reaction stages will govern at definite frequencies and such response reflected by EIS helps determine the limiting step rate. Thus, these should be avoided to obtain precise measurements.